Safe braking at a bike’s maximum potential deceleration, that’s what ABS provides. But how does motorcycle ABS work?
Safe braking at a bike’s maximum potential deceleration, that’s what ABS provides. After decades of development, Antilock Brakes are finally finding universal acceptance — even on sportbikes — and the technology is no longer considered a performance handicap. But how does motorcycle ABS work?
The maximum braking force a wheeled vehicle is able to achieve lies at a point just prior to lockup. But, the moment where the wheels will lock is infinitely variable and extremely difficult to predict. Each individual road surface has a unique coefficient of friction, which varies by temperature, weather and condition and the same goes for individual tires, factoring in wear and pressure too. Motorcycle dynamics also play a role as weight distribution changes under deceleration and the motorcycle leans over while cornering. Factor in a bike’s individual front and rear brakes and you have a very, very complicated equation.
And an important one.
Not only does the rate of deceleration achieved give us the ability to avoid stuff like left-turning cars, but if a wheel locks, it can cause the motorcycle to lose control and crash — even in non-emergency braking scenarios.
Until 1988 riders had no choice but to process that equation themselves, relying on “feel,” judgment and experience. Early ABS systems weren’t much of an improvement; while they were able to prevent wheels from locking, they often couldn’t achieve the same rate of deceleration as a reasonably skilled rider and were prone to kicking in when not needed. Thanks to the ever-increasing sophistication of computerized control units, modern ABS has improved to the point where its actuation is undetectable and its effectiveness is undeniable.
All ABS systems share the same basic components: Slotted rings on each wheel are used to monitor and compare wheel speeds, with the ABS ECU monitoring them constantly, at intervals just a tiny fraction of a second apart. But, the rider still actuates the brakes via hydraulic lines. On an ABS-equipped bike, the hydraulic pressure just flows through a pump controlled by that ECU and fitted with simple solenoid valves. If you pull the fuse that operates the ABS computer or pump, the brakes will still work, they’re mechanical, just with the ability for the electronics to intervene.
As technology advances, additional sensors supply the ECU with more data. Those sensors may include lean angle, handlebar angle, throttle position and the two separate brakes have started informing each other of their individual actions.
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There you are, riding along in the rain when — without warning and despite having a clear line of site to you — Nathan No Look pulls out in front of you at the last possible second. You grab a big handful of front lever and stomp on the back, slowing to a controlled halt as Nate continues his Twitter battle with sports fans from the rival team.
The reason you didn’t plow through his door and temporarily force him to look up from his phone was because the ABS ECU, during its constant monitoring and comparison of both wheel speeds, determined that a lock up was imminent and opened the pump’s valves to release pressure on the calipers, then modified the degree of pressure reaching them every hundredth of a second or so to optimally take advantage of what traction was available and hold you at a rate of deceleration just this side of wheel lock up. All you did was hang on to the levers and try not to urinate on yourself.
By comparing wheel speeds and the rate of change for each, the ABS ECU is able to effectively determine how hard it can allow the brakes to actuate, even without knowing what’s going on between the tires and the road surface.
That same basic function is what happens with any type of ABS. Some bikes add in brake linking, where hitting the front or rear lever may proportion some brake pressure to the other end, while others include an “off-road” mode designed to better work in low traction environments where some wheel lock is desirable. But, all that is taking place in the ECU’s electronic brain, not through a different mechanical spec or different actuation methods.
The reason ABS has become so extraordinarily effective is that it now benefits not only from vastly more data informing its actuation, but also with a greater capacity to quickly process that increased amount of data. The actual mechanical components of ABS remain virtually the same, but they do get smaller and lighter and better able to actuate quickly and finely thanks to advances in materials and production processes. The latest ABS systems add only 4.5 lbs to a bike’s weight, down from 10 lbs or more in the 1990s.
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On The Road
15 years or so ago, most bikes that had ABS were heavy tourers. Hit a lever hard enough to actuate an older bike’s ABS and you’d be met with a ton of lever pulsing as the system modulated brake pressure a few times a second. You could almost feel the rate at which it could process data. And while that detectable pulsing was able to prevent wheel lock up, it frequently failed to bring the bike to a halt in the same distance a decent rider would have been capable of on his or her own. It could also intervene too soon or in undesirable circumstances.
Jump forward about five years and that pulsing had disappeared, and the stopping distances moved inline with those of a very good rider, but ABS could still trigger where you didn’t want it to, such as while braking over tar snakes. This first modern generation of motorcycle ABS was also confounded by off-road conditions, so most bikes with any sort of dirt pretensions fitted with it came with a big “ABS Off” switch.
Nowadays, the technology has advanced so much that it’s nearly undetectable. You simply come to a controlled, rapid stop in the shortest distance possible. No pulsing, no second-guessing the efficacy, the bike is held at the absolute threshold of grip until you release the lever. Not only is it seamless, but up-to-date ABS delivers all the feel and control you’d get from a non-ABS bike, too. And, it works off-road. Sometimes. On the latest generation of ADV bikes, you can still catch ABS off-guard while attempting to shed speed on a steep descent, where you actually want full front brake lock. But, in general dirt riding, it works pretty well. Learn to ride with it — stop flying down steep descents and leaving braking till the last second — and it will actually add an element of safety. Particularly given the ever-expanding proportions and weights of that class of bikes, it’s a welcome addition.
The level of control and seamless precision of modern ABS even means that on the latest superbikes you can trail brake right up to the limit of a front tire’s grip, relying on the ABS to prevent you from washing the front.
The next generation — represented by Bosch Motorcycle Stability Control now entering production on the KTM 1190 Adventure — sees ABS work to prevent the bike from standing up under braking in turns.
Do You Want It?
Yes. The latest generation of ABS systems removes no control or feel from the rider and even the fastest racers will no longer be able to out-brake the computer, even in perfect conditions. In today’s horrifying traffic conditions, ABS is the last line of defense against careless drivers. On today’s hugely heavy Adventure bikes, it’s tuned to keep you upright even if you take them off-road. With modern ABS, your bike simply stops faster and more safely. That’s an advantage you need, whether you want to admit it or not.
Does your bike have ABS? Why or why not?
Has your experience with ABS been a good one?